Process for producing lithopone fast to light



Patented Dec. 4, 1928.

UNITED STATES PATENT OFFICE.

GUSTAV JANTSCH, OF BONN-(IN-THE-RHINE, AND PAUL WOLSKI, OF WIESDORF-ON- THE-RHINE, GERMANY, ASSIGNORS TO I, G. FARBENINDUSTRIE AKTIENGESELL- SCI-IAFT, F FRANKFORT, GERMANY.

PROCESS FOR PRODUCING LITHOIONE FAST T0 LIGHT.

No Drawing. Application filed November 3, 1924, Serial 110,747,671, and in Germany November 30, 1923.

As is known lithopone has the objectionable property of darkening in sunlight. It has been attempted to eliminate this property by several methods which however do not yield generally satisfactory results.

It has now been found that the presence of a Well defined small quantity of a compound of cobalt renders the lithopone fast to light and that the effective quantity thereof can be so small that the coloration-of the lithopone is not objectionably influenced. In general the quantity of the cobalt compound calculated as cobalt metal may vary from 0.02% to 0.5% of the zinc content of the lithopone.

The cobalt compound content of the lithopone may be provided for by carrying out the purification of the raw zinc salt -solutions from which the lithopone is to be precipitated in such a Way that small amounts of the heavy metal salts or compounds remain in the lithopone; or the heavy metal salts or compounds may be added to the zinc salt solution before or after purification; or'the desired suitable compounds may be added to the raw lithopone before ignition or after ignition c. g. during the Wet grinding.

Without attempting to ofler a conclusive main dissolved or similar quantities of nickel or cobalt salts are added tothe zinc salt solutions before or after purification.

Salts of copper or of iron may be used up to O,5%.

These salts of heavy metals may also be added to the precipitated or dried lithopone before or after ignition.

Mixtures of several salts or double salts of the heavy metals, such as nickel, cobalt, iron or copper may be used under similar conditions.

Example 2.3 grams of copper sulfate are added to the precipitated or dried crude lithopone, or'ignited lithopone (free from soluble sulfides) reckoned upon 1000 grams zinc in the lithopone and the copper sulfate is converted into copper oxide or copper sulfide by treatment with alkalies or sulfidizing agents.

We claim 1. Lithopone'which is fast to light containing a cobalt salt in quantity corresponding to from 0.02%to 0.5% by Weight ofcobalt metal calculated upon the zinc content of the lithopone.

2. Process for the production of lithopone which is fast to light, comprising adjusting the quantity of cobalt salt in the lithopone so that the weight of the cobalt metal contained therein corresponds to from about 0.02% to about 0.5% calculated upon the zinc content of the lithopone.

In testimony whereof we have hereunto set 

